Slice the flank steak into thin, bite-sized strips and season evenly with sea salt, black pepper, garlic powder, and smoked paprika.
Heat the avocado oil in a large cast-iron or stainless steel skillet over medium-high heat until shimmering.
Add the steak strips to the hot pan and sear for 2 to 3 minutes until browned and caramelized, then remove the steak from the pan and set aside.
In the same skillet, add the sliced bell peppers and red onion, sautéing for 4 to 5 minutes until they are tender and slightly charred.
Wipe the skillet clean and return it to medium heat.
Place the whole wheat tortilla in the skillet and sprinkle half of the shredded cheddar cheese onto one side of the tortilla.
Layer the seared steak and sautéed vegetables over the cheese, then top with the remaining cheese.
Fold the tortilla in half and cook for 2 minutes per side, pressing down gently, until the tortilla is golden brown and the cheese is fully melted.
Remove from the pan, let it rest for one minute, then slice into three wedges and serve.